This invention relates to reproduction machines, in general, and particularly to such a machine having a high capacity cassette tray assembly for effectively and reliably holding and positioning stacks of sheets for feeding within the reproduction machine.
Reproduction machines include but are not limited to electrostatographic process machines. Generally, the process of electrostatographic reproduction machines includes uniformly charging an image frame of a moving photoconductive member, or photoreceptor, to a substantially uniform potential, and imagewise discharging it or imagewise exposing it to light reflected from an original image being reproduced. The result is an electrostatically formed latent image on the image frame of the photoconductive member. For multiple original images, several such frames are similarly imaged. The latent image so formed on each frame is developed by bringing a charged developer material into contact therewith. Two-component and single-component developer materials are commonly used. A typical two-component developer material comprises magnetic carrier particles, also known as "carrier beads," having fusable charged toner particles adhering triboelectrically thereto. A single component developer material typically comprises charged toner particles only.
In either case, the fusable charged toner particles when brought into contact with each latent image, are attracted to such image, thus forming a toner image on the photoconductive member. The toner image is subsequently transferred at a transfer station to an image receiver copy sheet. The copy sheet is then passed through a fuser apparatus where the toner image is heated and permanently fused to the copy sheet forming a hard copy of the original image. The copy sheets typically are held and positioned (for feeding to the transfer station) in a motorized elevator sheet supply assembly within the machine, or in a non-motorized portable or removable spring and pivot cassette tray assembly.
Conventional non-motorized spring loaded and pivoting type cassette trays or tray assemblies are well known. Typically, forward feed corner snubber type cassette trays can effectively hold and position only up to a maximum of 250 sheets per full tray for feeding in image reproduction machines. The following patents disclose examples of such cassette trays.
U.S. Pat. No. 4,591,141 entitled "First Point Sheet Feeder", discloses a sheet feeder that is pivotably mounted so that the paper supply is maintained in contact with a fixed portion feed roller. The sheet feeder's pivot point is selected to provide constant feed pressure to the paper supply regardless of the size of the remaining paper supply.
U.S. Pat. No. 4,358,102 entitled "Copy Paper Feeding Cassette" discloses a cassette that has a cutout or gate centrally defined in each wall of the cassette. The cassette also has a reinforcing plate pivotally mounted at a forward portion of each side wall. Upon mounting in a machine, the reinforcing plates bridge the cutouts or gate and cooperate with machine members to prevent skewed feeding of a topmost sheet.
U.S. Pat. No. 3,599,972 entitled "Paper Tray for Photocopy Machine" discloses a floating feed tray including a pair of feed rollers positioned above the forward end of the tray and mounted on a fixed axis. The rearward end of the tray is biased downwardly to pivot the tray about a pivot point so as to raise the forward end to bring the topmost sheet into feeding engagement with the feed rollers.
JP 47-146600 (Canon KK) Sep. 9, 1974, Utility Model discloses a paper feeding cassette including a sheet separating pivot or snubber that shifts from the paper feeding positions when sheets are being loaded.
U.S. Pat. No. 3,408,064 entitled "Auxiliary Paper Tray for Copying Machine" discloses a paper tray that has lateral and end guides or walls that are fixedly attached to the bottom plate of the tray to accommodate a stack of sheets.
Such non-motorized conventional cassette trays, for example, those that have forward feed corner snubbers cooperating with a feed roller, are very sensitive to a sheet feeding angle of the top of a stack of sheets relative to the feed roller and the corner snubbers. The effectiveness and reliability of sheet feeding from such a cassette tray are also very sensitive to the penetration distances or displacement made by the cooperating feed roller into a stack of sheets during a feed stroke of the feed roller or wheel. Such sensitivities have ordinarily limited the size of any stack of sheets that can be held by such a tray. For example, a stack of standard 20# sheets is ordinarily limited to 250 sheets or less.
There has therefore been a need for a relatively low cost, and reliable feed roller and corner snubber type cassette tray that can hold and position stacks of sheets greater than the ordinarily limited 250 sheet maximum.